For many years it has been theorized that stratification of the charge in an internal combustion engine combustion chamber has the potential for providing more positive ignition and more complete combustion of air-fuel mixtures than use of a homogeneous charge arrangement, thus yielding the possibility of both improved engine efficiency and reduced emissions of unburned combustibles with stratified charge. Proposed combustion chamber arrangements have taken many forms, including what I have called rich-core stratified charge arrangements in which each combustion chamber is provided with a preferably swirling charge having a central core of relatively fuel-rich mixture (which may be leaner than stoichiometric) and a surrounding peripheral portion composed primarily of air or leaner mixture. Examples of such arrangements are found in my prior U.S. Pat. Nos. 4,014,300 granted Mar. 29, 1977, 4,018,193 granted Apr. 19, 1977, and 4,119,064 granted Oct. 10, 1978, all of which are assigned to the assignee of the present invention.